As is well known in the art, electrical and electronic applications can utilize electrical filters to suppress undesirable signals, such as electrical noise and ripple. Such filters are designed to prevent the propagation of unwanted frequency components from the filter input port to the filter output port, while passing desirable components. Low-pass filters, which pass relatively low frequency signals, typically employ capacitors as shunt elements, and may include inductors or other components as series elements. Illustrative prior art filter arrangements are shown in FIGS. 1A-C.
The attenuation of a filter stage can be determined by the amount of impedance mismatch between the series and shunt paths. For a low-pass filter, it is generally desirable to minimize shunt-path impedance and maximize series-path impedance at high frequencies.
However, the performance of such filters can be degraded by the filter capacitor parasitics. Parasitic effects refer to effects that cause the component to deviate from its ideal or desired characteristic. FIG. 2 shows a prior art first order model for a conventional filter capacitor CF including the equivalent series resistance (ESR), RESR and equivalent series inductance (ESL), LESL, of the capacitor. FIG. 3 illustrates the impedance characteristic of a typical prior art capacitor across frequency. As can be seen, at higher frequencies the capacitor impedance is dominated by the ESL. For example, a typical aluminum electrolytic capacitor may appear inductive (impedance rising with frequency) at frequencies above 50-100 kHz, thereby limiting its ability to shunt ripple at high frequencies.
One prior-art approach for overcoming filter capacitor limitations is to couple capacitors of different types in parallel (to cover different frequency ranges) and/or to increase the order of the filter used (e.g., by adding series filter elements such as inductors). While these approaches can reduce parasitic effects to some extent, they can add considerable size, complexity, and cost to the filter.
It would, therefore, be desirable to provide a component and filter that overcome the aforesaid and other disadvantages.